Process for the catalytic oxidation of organic compounds



May 18, 1937. B. M. REYNOLDS 2,081,120

'PROCESS FOR THE CATALYTIC OXIDATION OF ORGANIC COMPOUNDS Filed April 20. 1929 i .gi/n nfor .Mr/Y

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PROCESS FOR THE CATALYTIC OXIDATION OF ORGANIC COMPOUNDS Blyth M. Reynolds, Utica, N. Y.

Application April 20, 1929, Serial No. 356,851

4 Claims.

My invention relates to a process for the catalytic oxidation of organic compounds and I declare the following to be a. full, clear, concise and exact description thereof sumcient to enable anyone skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawing in which like characters refer' to like parts throughout the speciiication.

The invention relates particularly to an improvement in the method of regulating and controlling temperature in the production of partial oxidation products of organic aromatic compounds such as phthalic anhydride from naphthalene, anthraquinone from anthracene, benzaldehyde from toluol, and other organic compounds by oxygen containing gas. The production of the aforesaid mentioned products or compounds is effected usually by the catalytic oxidation of aromatic hydrocarbons in the vapor stage with an oxygen containing gas.

'Ihe control, however, of reactions involving the partial oxidation of aromatic hydrocarbons with an oxygen containing gas, which reactions are for the most part exothermic, is accompanied with best results by the use of a boiling medium brought into a heat transferring relationship to the reaction zone of the catalytic agent or catalyzer whereby the heat generated by the reaction is withdrawn as soon as it is formed by the evaporation of the medium. The invention has, therefore, particular reference to the material used as the boiling medium and is designed to accomplish such heat control with a high degree of accuracy in the particular kind of processes pointed out above and generally in the operation of processes where substances in the vapor state react with each other and where an exact control of the reaction temperature is of prime importance for an economic yield of the process. Furthermore, it avoids the disadvantages experienced with boiling heat exchange mediums heretofore used as for instance sulphur or mercury, or the alloys of mercury.

Mercury and mercury alloy have been used heretofore in such heat exchange mediums; they are unsatisfactory, however, for the reason that mercury when heated to the boiling point, emits poisonous fumes, which seriously react with deleterious eiect upon the human system. This is so even in those processes which operate without pressure to vary the temperature of the heating medium where there is little chance for the escape joints are sealed to prevent the escape of the mercury fumes, but in systems operating without pressure the joints mightenot be so tight and thereby leave open the possibility of the accidental escape of the mercury fumes. In either case, however, whether sealed or unsealed, it is desirable to avoid the use of mercury, for the above reason, asone of the elements of the heat transferring medium. Another reason why the use of mercury should be avoided is its relatively high costs in comparison with the medium forming part of this invention.

Sulphur has been used also as a heat transferring medium but with unsatisfactory results for the reason that boiling sulphur which is considerably more corrosive than liquid sulphur at lower temperature. Its use, therefore, presents structural diiculties. By actual experience I may state that boiling sulphur, used in calorized steel converters has corroded said converters to such an extent that within two months they were iron and that this sulphide coats the surface of the converter with a scale that acts as an insulating medium, the eiect of the heat control thereby being greatly diminished.

The use of a converter constructed from material other than iron alloys is restricted either because of their known lack of resistance to the corrosive eilect of boiling sulphur or because of their known low tensile strength at high temperatures.

In place of either mercury or sulphur to eiect the desired result, this invention contemplates the use of condensed hydrocarbons such as diphenyl which is now manufactured on a large scale by heating benzol under predetermined conditions in such manner as to cause two benzene molecules to combine. Diphenyl oiers the advantages that it is stable even when heated to 500 degrees centigrade and above and under a pressure of 400 lbs. per square inch and over, which is the degree of pressure required to raise its boiling point to about 500 C. Moreove diphenyl has the further advantage of being noncorrosive on metals under any conditions of heat or pressure. Furthermore, it has certain physical properties that are desirable in controlling the temperature of the heating medium in processes of partial oxidation of organic compounds where carried at a range from 255 to 500 C. and over. The boiling pointl of diphenyl is approximately 255 degrees centigrade at 'atmospheric pressure.

The desired temperature, therefore, can be attained by varying the pressure to the predeter mined degree to effect an accurate control of the temperature, of the reacting gases which is one of the salient features desired in processes of this nature.

By the use of diphenyl the whole gamut of pressures reaching 430 lbs. per square inch at a boiling point of approximately 500 degrees centigrade is possible and quite practical. Moreover, the latent heat of vaporization of diphenyl is very low comparatively, and varies inversely to the ratio of the increase of its temperature, ranging from about 150 British thermal units per pound at 255 degrees centigrade to about l'Z0 British thermal units per pound at 500 degrees centigrade. This fact is an advantage with an exothermic reaction for the reason that the diphenyl, which acts as the heat transferring medium, is quickly brought to a vigorous boiling condition, whereby an even or constant distribution of heat throughout the apparatus, as well as an increase in the rate of heat transfer through the catalyst tube surfaces is assured. Diphenyl allows, therefore, a novel flexible control of the temperature of the partial oxidation process that is preferable to those heretofore used.

The object will be better understood by referring to the drawing in which:

Fig. l is a perspective view of the device used in the process.

Fig. 2 is a section of the converter used in the process.

Referring more particularly to the drawing, an apparatus is employed that allows bringing a reaction mixture in gaseous or vapor form into contact with a catalyst, which is arranged in heat transferring relationship with diphenyl.

To this end a converter of cylindrical shape is represented by I; there is a dome or spherical segment top part 2 with an annular flange 3, whereby it is riveted in a hermetically air tight manner to the annular flange 4 that is brazed or welded to the top edge of the converter I. An asbestos gasket 5 is disposed between the contacting surfaces to aid in sealing said parts.

Referring more particularly to the drawing, an apparatus is employed that allows bringing a reaction mixture in gaseous or vapor form into contact with a. catalyst, which is arranged in heat transferring relationship with diphenyl.

To this end a converter of cylindrical shape is represented by I; there is a dome or spherical segment top part 2 with an annular flange 3, whereby it is riveted in a hermetically air tight manner to the annular flange 4 that is brazed or welded to the top edge of the converter I. An asbestos gasket 5 is disposed between the contacting surfaces to aid in sealing said parts.

Likewise, a spherical segment I 0 is secured to the lower edge II of converter I, flange I2 by means of the flanged edge I3 of said segment I0. An inlet pipe I4 is riveted, or otherwise secured, in hermetically air tight manner to the surface of top 2 adjacent its center and an outlet pipe I5 is likewise secured to the center of lower spherical segment part I0.

Upper pipe I4 is connected to a tank, not shown, containing the organic compound and oxidizing gas, whereas the reaction products together with the unreacted organic compound and the gas, containing an excess of oxygen, pass out of the converter I through outlet pipe I5 to other well known methods. A plurality of catalyst tubes 20 are supported at either end in vertical position within converter I by tube sheets 2|, 22, which are provided with apertures to allow for the passage of the gases subjected to the catalytic reaction therethrough and through the corresponding catalyst tubes 20. Tube sheets 2|, 22 are brazed or welded to the inner surface of converter I. All joints in connection with the catalyst tubes 20, as well as other joints are hermetically sealed. A screen 23 is supported below tube sheet 22 by angle brackets 24 and is adapted to hold the catalyst, which may be an oxide of rare metals, such as vanadium, within said tubes 20. Tubes 2li above the level of the catalyst may be empty or fllled with porous non-catalytic mass.

Reflux pipes 25 are connected to the upper part of converter I and lead to an expansion or`pressure tank 26, so as to allow a suillcient gas volume to compensate for small variations due to conditions in the system and not to seriously alter or disturb the pressure in the space above the diphenyl converter which would affect the predetermined boiling point of the diphenyl. Pressure tank 26 is piped at 21 to a cylinder 28 of inert gas such as nitrogen or carbon dioxide with any well known pressure regulating valve 30 interposed in said pipe 21. 'I'he proper adjustment of the regulating valve 30 will control the pressure on the diphenyl and hence its boiling point. Water jackets 32, 32 are disposed about reflux pipes 25, 25 to aid in condensing the gases passing therethrough. A safety outlet and valve is provided at 33. A heating pipe 34 is disposed through converter I and between tubes 20 whereby to apply external heat into the diphenylin the event it is found necessary to maintain the proper temperature for the chemical reaction in the catalyst tubes 20.

In order to effect a catalytic reaction, the organic compound to be oxidized together with the oxygen containing gas enters the converter I through inlet pipe I4 and passes down through the catalyst in tubes 20 where the reaction takes place. The heat generated by this chemical reaction is transferred through the walls, which are good heat conductors, of tubes 20 to the diphenyl that fills the spaces about tubes 20. The height or level of the diphenyl bath is kept above the level of the catalyst in tubes 20 as illustrated in dotted lines in Fig. 2. A distributing space 35 is provided above tubes 20, whereby to permit the organic compound and oxygen containing gases entering through inlet pipe I4 to expand and pass equally through catalyst tubes 20 where the chemical reaction takes place. The reaction products together with the unreacted organic compound and the gas, containing an excess of oxygen pass out of the converter I through pipe I5 to other apparatus where the valuable constituents are recovered as above stated.

Having thus described my invention what I claim to be new and desire to secure by letters Patent is as follows:

1. In the production of partial oxidation products from organic compounds in the vapor phase with an oxygencontaining gas in the presence of a catalyst, that part of the process comprising arranging the catalyst and the reacting gases in heat transferring relationship with diphenyl, and applying pressure to the diphenyl in order to regulate the boiling point of the same.

2. In the production of partial oxidation products from organic compounds in the vapor phase with an oxygen containing gas in the u presence of a catalyst, that part of the process comprising arranging the catalyst, and the reacting gases in heat transferring relationship with diphenyl thereby vaporizing the same, and regulating the boiling point of the same by pressure to approximately the temperature of the oxidation process.

3. In the production of partial oxidation products from organic compounds in the vapor phase with an oxygen containing gas in the presence of a catalyst, the step of bringing diphenyl in heat transferring relation with the reaction zone.

4. In a. process for producing benzaldehyde and benzoic acid by the vapor phase catalytic oxidation oi' toluol with an oxygen containing gas in the presence of a catalyst that part of the process which comprises controlling the temperature of the reaction in the catalyst zone by means of abath of boiling diphenyl in a heat transferring relation to the reaction zone, the diphenyl bath being kept at a constant boiling temperature by subjecting it to pressure, and the heat transferred to the diphenyl being removed by condensing the vapors of said diphenyl and returning the condensate continuously to the boiling diphenyl.

BLYTHE M. REYNOLDS. 

